Bag filters are typically formed from sheets of flexible material which are joined together, usually by sewing such sheets together. For example, bag filters prepared from high dirt capacity polypropylene filter media sheets which have been sewn together are commercially available from Pall Corporation (Glen Cove, N.Y.) under the trademark Profile.RTM..
While in most uses the sewn seams of such bag filters do not affect the integrity of the bag filters, there are some instances in which the sewn seams of conventional bag filters can become leakage pathways depending upon the nature of the fluids being filtered and the pressure at which filtration is being effected. Although sewn seams may sometimes become leakage pathways, thereby allowing unfiltered fluid to bypass the filter media, the prevailing conventional practice of preparing bag filters continues to involve sewn seams. This preference is the result of the need for the existence of a strong mechanical bond between the filter medium portions joined together to form the bag filter so as to enable such bag filters to be used in rugged environments. Such a strong mechanical bond cannot generally be provided by gluing or heat-sealing the filter medium sheets instead of stitching such sheets together. The published prior art literature similarly discloses the prevailing preference of using stitching to prepare bag filters and the like.
For example, U.S. Pat. No. 3,422,602 discloses a bag filter for a gas cleaning apparatus. The bag filter is formed of filter material sheets, such as glass fiber layers, which are stitched together so as to compress the filter material sheets and form substantially air-tight seams. As an alternative, instead of stitching the edges of the filter material sheets together, the edges may be glued or heat-sealed together.
Similarly, U.S. Pat. No. 4,959,045 discloses a method of making a filter sock, wherein the projecting side of a panel of two leaves is folded back over the free side and the sides are sewn together to form a tube.
There remains, therefore, a need for a bag filter with seams constructed in such a manner so as not to allow the fluid being filtered to bypass the filter medium by way of the seams, while at the same time providing for a good mechanical bond at the bag filter seams. The present invention provides such a bag filter.